The present invention relates to a fluid flow rate detecting technique, and particularly to a flowmeter for determining the flow rate or integrated flow rate of fluid such as gas, liquid or the like and a flow rate sensor unit for use in the same, and a flow rate sensor for detecting the flow rate of fluid flowing in a pipe.
There have been hitherto used various types of flow rate sensors (or flow velocity sensors) for determining the flow rate (or flow velocity) of various kinds of fluid, particularly liquid, and a so-called thermal type (particularly, indirectly heated type) flow rate sensor has been used because the price thereof can be reduced.
There is used an indirectly heated type flow rate sensor in which a sensor chip having a thin film heater and a thin film temperature sensor laminated on a substrate through an insulating film by using the thin film technique is disposed so that heat can be transferred between the sensor chip and fluid in a pipe. By supplying current to the heater, the temperature sensor is heated to vary the electrical characteristic of the temperature sensor, for example, the value of the electrical resistance. The variation of electrical resistance value (based on temperature increase of the temperature sensor) is varied in accordance of the flow rate (flow velocity) of fluid flowing in the pipe. This is because a part of the heating value of the heater is transferred into the fluid, the heating value dispersed into the fluid is varied in accordance with the flow rate (flow velocity) of the fluid, and thus the heating value supplied to the temperature sensor is finally varied in accordance with the flow rate (flow velocity) of the fluid, so that the electrical resistance value of the temperature sensor is varied in accordance with the flow rate (flow velocity) of the fluid. The variation of the electrical resistance value of the temperature sensor is also different in accordance with the temperature of the fluid, and thus a temperature sensor for temperature compensation is installed in an electrical circuit for detecting the variation of the electrical resistance value of the temperature sensor to suppress the variation of the flow rate measurement value due to the temperature of the fluid as much as possible.
For example, an indirectly heated type flow rate sensor using a thin film element disclosed in JP(A)-8-146026, which is estimated to be excellent in thermal response, high in measurement precision, compact in size and low in cost, has the following construction.
That is, as shown in FIGS. 24A and 24B, a flow rate sensor 501 has a thin film heater 503 and a thin film temperature sensor 504 which are laminated on a substrate 502 through an insulating layer 505 by using the thin film technique, and it is used while disposed at a proper position of a pipe 506 as shown in FIG. 25.
In the flow rate sensor 501, the temperature sensor 504 is heated by supplying current to the heater 503 to detect the variation of the electrical resistance value of the temperature sensor 504. Since the flow rate sensor 501 is disposed in the pipe 506, a part of the heating value of the heater 503 is dispersed through the substrate 502 to the fluid flowing in the pipe, and thus the heating value transferred to the temperature sensor 504 corresponds to the value achieved by subtracting the dispersed heating value from the heating value of the heater 503. Further, since the dispersed heating value is varied in accordance with the flow rate of the fluid, the flow rate of the fluid flowing in the pipe 506 can be determined by detecting the variation of the electrical resistance value of the temperature sensor 504 which varies in accordance with the heating amount being supplied thereto.
Furthermore, since the dispersed heating value is also varied in accordance with temperature, a temperature sensor 507 is disposed at a proper position of the pipe 506 as shown in FIG. 25, and a temperature compensating circuit is added in the flow rate detecting circuit for detecting the variation of the electrical resistance value of the temperature sensor 504 to reduce the error of the flow rate measurement value due to the temperature of the fluid at maximum.
However, the conventional flow rate sensor 501 is directly mounted on the metal pipe 506, and also the metal pipe 506 is exposed to the outside air. Therefore, the heating value of fluid itself is dispersed to the outside air through the metal pipe having high thermal conductivity, or the heating value of the outside air is liable to be supplied to the fluid, resulting in reduction in the measurement precision of the flow rate sensor 501. Particularly when the flow rate of fluid is very low, it has a great effect on the measurement precision, and thus when the temperature difference between the fluid and the outside air is large or when the specific heat of the fluid is small, the effect is more remarkable.
When the fluid is viscous fluid, particularly viscous fluid having relatively high-viscosity, particularly liquid, the flow velocity in the cross-section perpendicular to the flow direction of the fluid in the pipe 506 is largely different between the portion in the neighborhood of the pipe wall and the center portion, and the flow velocity vector exhibits a substantially parabolic distribution having the extreme value at the center portion. That is, the non-uniformity of the flow velocity distribution is remarkable.
In the case where the substrate 502 or a casing 508 connected to the substrate 502 is merely mounted on the pipe wall and exposed to the fluid to detect the flow velocity at only the portion in the neighborhood of the pipe wall as described above, the flow velocity distribution has a large effect on the precision of the flow rate measurement. This is because no consideration is given to the flow velocity of fluid flowing at the central portion in the cross-section of the pipe and consideration is given to only the flow velocity of fluid flowing in the neighborhood of the pipe wall of the pipe. As described above, when the fluid is viscous fluid having relatively high viscosity, the conventional flow rate sensor has a problem that it is difficult to accurately determine the flow rate. Even when the fluid has low viscosity at normal temperature, the viscosity increases as the temperature is reduced, so that the problem associated with the fluid viscosity as described above occurs. Particularly, the above problem based on the viscosity is more remarkable when the flow rate per unit time is relatively small than when the flow rate per unit time is large.
Further, the flow rate sensor 501 is used under various different environments such as geographical conditions, indoors/outdoors, etc., and various other factors such as season conditions, day/night, etc. are also added particularly outdoors, so that consideration must be given to temperature variation due to external environments. However, the conventional flow rate sensor 501 is designed to be likely influenced by such external environmental temperature, so that the measurement value of the flow rate has a large error. Therefore, a flow rate sensor that can determine the flow rate with high precision under broad external environmental temperature has been required.
In order to solve this problem, a flow rate sensor as shown in FIG. 26 has been proposed. This is substantially the same as disclosed in JP(A)-11-118566, for example.
In FIG. 26, a flow rate detector 306 having a thin film heater and a thin film temperature sensor which are laminated on a substrate 302 through an insulating layer is mounted on a horizontal portion 307a of a fin plate 307 which is bent in an L-shape, thereby forming a flow rate sensor 301. In a casing 308, glass 310 is sealingly filled between the vertical portion 307b of the fin plate 307 and the opening portion of a flow pipe 309, and the flow rate detector 306 and the overall horizontal portion 307a of the fin plate 307 are hermetically coated and fixed by synthetic resin 311. The upper portion of the casing 308 is covered by a lid 312.
Reduction in the measurement precision of the flow rate due to the dispersion of heating value to the outside air or supply of heating value from the outside air, variation of flow rate in the lateral cross-section of the pipe, the effect of the external temperature environment, etc. can be greatly overcome by the flow rate sensor 301 described above.
However, in the above flow rate sensor 301, the flow rate detector 306 and the synthetic resin 311 are directly brought into contact with each other, so that the heating value owned by the temperature sensor flows out to the synthetic resin 311 or the heating value flows from the synthetic resin 311 into the temperature sensor. Further, the flow rate detector 306 is joined to the horizontal portion 307a of the fin plate 307 by joint material 313 of silver paste having excellent thermal conductivity or the like, so that the heating value transferred through the fin plate 307 flows out to the synthetic resin 311 through the joint material 313, or the heating value flows out from the synthetic resin 311 to the fin plate 307. Accordingly, when the specific heat of the fluid is small or when the flow rate is low, the sensitivity of the flow rate sensor 301 may be reduced.
Besides, the glass 310 is filled between the vertical portion 307b of the fin plate 307 and the opening portion of the flow pipe 309 to intercept the thermal transfer. However, when the fin plate is minutely vibrated due to the fluid flow and the sealing state becomes imperfect, the heating value transferred through the fin plate 307 flows out to the casing 308 through the metal flow pipe 309 having excellent thermal conductivity or the heating value flows from the casing 308 into the fin plate 307. Accordingly, when the specific heat of the fluid is small or when the flow rate is low, the sensitivity of the flow rate sensor 301 may be reduced as in the foregoing case.
The present invention has an object to solve the above problem and provide a flow rate sensor that can suppress flow-in/flow-out of heating value between each part of the flow rate sensor and a casing/the external to determine the flow rate with high precision even when the specific heat of fluid is small, when the flow rate is low, etc., and can be easily fabricated and reduced in cost.
The flow rate sensor disclosed in the above JP(A)-11-118566 uses an electrical circuit containing a bridge circuit to achieve the electrical output corresponding to the flow rate of fluid.
In general, the output of the electrical circuit of the flow rate sensor has no simple proportional relationship with the flow rate value. Therefore, in order to convert the output of the electrical circuit to the flow rate value, data processing using a calibration curve may be carried out. The data processing is carried out by using a microcomputer, and digital signals indicating the flow rate value may be input to a display device or transmitted to a desired remote place through a communication line.
However, with respect to the flow rate sensor as described above, it is required to throw the contact portion thereof with fluid and the surrounding portion thereof away periodically or after a predetermined amount of fluid flows. For example, when the flow rate sensor is applied to determine the flow rate of raw materials in a process of synthesizing high-purity reagent or medicines, throw-away is required from the viewpoint of surely preventing purity-reduction of products due to contamination of impurities. Further, when it is applied to a flow rate measurement of samples in a chemical analysis such as chemical titration or the like, throw-away is required from the viewpoint of preventing an adverse effect on the analysis due to unexpected chemical reactions because the components contained in the samples are unknown. Still further, when it is applied to a flow rate measurement of liquid medicines being injected into a living body or a flow rate measurement of a body fluids picked up from a living body, throw-away is required from the viewpoint of preventing disease infection.
Actually, the throw-away portions have been strongly required to be miniaturized in size and reduced in cost. Therefore, it has been considered to unify a thermal conductor to be extended into a fluid flowing pipe, a sensor chip fixed to the thermal conductor and wires connected to the terminals of the sensor chip into a unit as a throw-away portion.
However, in this case, the following problem occurs. That is, when a sensor unit thus unified as described above is used as a disposable unit, a common calibration curve is used for plural sensor units in a data processing circuit to convert the output of the electrical circuit to the flow rate value. The calibration curve regulates-a standard relationship, and no consideration is given to an individual condition of each sensor. However, actually, the orientation of the thermal conductor to be extended to the external, the joint state between the sensor chip and the thermal conductor, the connection state between the sensor chip and the wires are minutely varied every sensor unit, and thus the relationship between the flow rate supporting output and the flow rate value is frequently varied every sensor unit. In this case, a measurement error occurs in the flow rate measurement due to the individual difference among sensor units, and thus the measurement precision is reduced.
Therefore, an object of the present invention is to provide a flow rate sensor unit which can suppress occurrence of a flow rate measurement error due to the individual difference of sensor units.
Further, another object of the present invention is to provide a flowmeter which can suppress occurrence of a flow rate measurement error due to the individual difference of sensor units.
In order to attain the above objects, according to the present invention, there is provided a flow rate sensor unit in which a flow rate detector having a heater and a flow rate detecting temperature sensor is joined to a flow rate detecting thermal conductor, and the flow rate detector and a part of the flow rate detecting thermal conductor are accommodated in a housing, characterized in that the housing encloses a memory for storing individual information of the flow rate sensor unit used when a flow rate value is achieved on the basis of a detection signal of a detecting circuit containing the heater and the flow rate detecting temperature sensor, and the flow rate detector and the memory are connected to plural leads in the housing, the plural leads being partially exposed to the outside of the housing.
In an aspect of the present invention, a fluid temperature detector containing a fluid temperature detecting temperature sensor is joined to a fluid temperature detecting thermal conductor, the housing encloses the fluid temperature detector and a part of the fluid temperature detecting thermal conductor, the detecting circuit contains the fluid temperature detecting temperature sensor, and in the housing the fluid temperature detector is connected to plural leads which are partially exposed to the outside of the housing.
In an aspect of the present invention, the individual information stored in the memory is correction information for a standard calibration curve used when the flow rate value is achieved on the basis of the detection signal of the detecting circuit.
In an aspect of the present invention, a fluid channel is connected to the housing, and the other part of the flow rate detecting thermal conductor extends into the fluid channel. In an aspect of the present invention, a fluid channel is connected to the housing, and the other part of the fluid temperature detecting thermal conductor extends into the fluid channel.
In order to attain the above objects, according to the present invention, there is also provided a flowmeter including the above flow rate sensor unit and an electrical circuit portion connected to the leads of the flow rate sensor unit, wherein the electrical circuit portion achieves the fluid flow rate value on the basis of the detection signal of the detecting circuit by referring to a standard calibration curve stored in advance, and at that time corrects the standard calibration curve by using the individual information stored in the memory of the flow rate sensor unit.
In an aspect of the present invention, the electrical circuit portion includes an analog circuit portion for achieving the output corresponding to the flow rate of the fluid by using the detection signal of the detecting circuit, and a digital circuit portion for achieving the fluid flow rate value on the basis of the output of the analog circuit, and the digital circuit portion includes a microcomputer and a main memory for storing the standard calibration curve.
In an aspect of the present invention, the individual information stored in the memory of the flow rate sensor unit reflects plural relationships between the output value corresponding to the fluid flow rate actually-measured for the flow rate sensor unit and the true fluid flow rate value.
In an aspect of the present invention, the leads of the flow rate sensor unit and the electrical circuit portion are detachably connected to each other.
In order to attain the above objects, according to the present invention, there is also provided a flow rate sensor unit in which a flow rate detector having a heater and a flow rate detecting temperature sensor is joined to a flow rate detecting thermal conductor, and the flow rate detector and a part of the flow rate detecting thermal conductor are accommodated in a housing, characterized in that a fluid channel is connected to the housing, the other part of the flow rate detecting thermal conductor extends into the fluid channel, a thermal conductor extending from the inside of the housing into the fluid channel is disposed, the housing encloses a memory for storing individual information of the flow rate sensor unit used when a flow rate value is achieved on the basis of a detection signal of a detecting circuit containing the heater and the flow rate detecting temperature sensor, and the flow rate detector and the memory are connected to plural leads in the housing, the plural leads being partially exposed to the outside of the housing.
In an aspect of the present invention, a fluid temperature detector containing a fluid temperature detecting temperature sensor is joined to a fluid temperature detecting thermal conductor, the housing encloses the fluid temperature detector and a part of the fluid temperature detecting thermal conductor, the other part of the fluid temperature detecting thermal conductor extends into the fluid channel, the detecting circuit contains the fluid temperature detecting temperature sensor, and in the housing the fluid temperature detector is connected to plural leads which are partially exposed to the outside of the housing.
In an aspect of the present invention, the individual information stored in the memory is correction information for a standard calibration curve used when the flow rate value is achieved by using the detection signal of the detecting circuit.
In an aspect of the present invention, the thermal conductor extends to be nearer to the portions of the leads in the housing than the flow rate detecting thermal conductor. In an aspect of the present invention, the thermal conductor extends to be nearer to the portions of the leads in the housing than the fluid temperature detecting thermal conductor.
In an aspect of the present invention, the memory is joined to the thermal conductor.
In an aspect of the present invention, the flow rate detecting thermal conductor, the fluid temperature detecting thermal conductor and the thermal conductor are designed in a plate shape, and arranged along the direction of the fluid channel on the same plane in the fluid channel.
In order to attain the above objects, according to the present invention, there is also provided a flowmeter containing the above flow rate sensor unit and an electrical circuit portion connected to the leads of the flow rate sensor unit, wherein the electrical circuit portion achieves the fluid flow rate value on the basis of the detection signal of the detecting circuit by referring to a standard calibration curve stored in advance, and at that time corrects the standard calibration curve by using the individual information stored in the memory of the flow rate sensor unit.
In an aspect of the present invention, the electrical circuit portion includes an analog circuit portion for achieving the output corresponding to the flow rate of the fluid by using the detection signal of the detecting circuit, and a digital circuit portion for achieving the fluid flow rate value on the basis of the output of the analog circuit, and the digital circuit portion includes a microcomputer and a main memory for storing the standard calibration curve.
In an aspect of the present invention, the individual information stored in the memory of the flow rate sensor unit reflects plural relationships between the output value corresponding to the fluid flow rate actually-measured for the flow rate sensor unit and the true fluid flow rate value.
In an aspect of the present invention, the leads of the flow rate sensor unit and the electrical circuit portion are detachably connected to each other.
In order to attain the above objects, according to the present invention, there is also provided a flow rate sensor comprising a flow rate measuring portion for detecting the flow rate of fluid, a temperature compensating measuring portion for compensating an effect of fluid temperature on measurements of the flow rate measuring portion, and a housing, wherein the flow rate measuring portion includes a flow rate detector having a heater and a temperature sensor laminated each other through an insulator, a fin plate joined to the flow rate detector at one end thereof, and an output terminal electrically connected to the flow rate detector, the temperature compensating measuring portion includes a temperature detector having an insulator and a temperature sensor that are laminated on each other, a fin plate joined to the temperature detector at one end thereof, and an output terminal electrically connected to the temperature detector, the housing encloses the flow rate detector and the temperature detector therein, and the fin plates and the output terminals of the flow rate measuring portion and the temperature compensating measuring portion are projected to the outside of the housing.
The housing is preferably formed of synthetic resin having thermal conductivity of 0.7 W/mxc2x7K or less. In the flow rate sensor according to the present invention, it is preferable that a cavity portion is provided in the housing, and the flow rate detector and the temperature detector are mounted at a position of the cavity portion at which the flow rate detector and the temperature detector are not brought into contact with the housing.